Railroad freight car draft gears have been used for many years at opposite ends of a railcar to absorb and cushion impact forces. Most railcar draft gears include a housing having an inner tapered bore at an open end, an elongated spring disposed within the housing, a series of metal friction shoes or members arranged in the tapered bore of the housing and movable against the spring upon compression of the draft gear, and a wedge or actuator disposed in operable combination with the friction members such that impact blows directed against the wedge are transferred axially to the spring and radially to the housing. In most railcar draft gears, a spring seat is arranged between an end portion of each friction member and the spring.
Recently, elastomeric materials have been used and accepted as replacements for steel springs. One elastomeric spring assembly offering beneficial results is disclosed in U.S. Pat. No. 5,351,844 to R. A. Carlstedt and includes multiple elastomeric spring pads stacked in axial relation relative to each other. Such a spring assembly has been successfully used for years in combination with railcar draft gears.
During their operation, and particularly while assembling a train consist in a railyard, the railcars experience high impact loads. While conventional draft gears have high shock absorbing capacities and capabilities, it is desirable for such draft gears to furthermore operate such that they absorb and return forces imparted thereto over a relatively consistent hysteretric force/travel curve which is relatively free from impact spikes.
Besides absorbing, storing and returning energy, one of primary functions of the draft gear spring is to maintain the friction shoes in sliding relationship relative to the inner tapered bore in the draft gear housing. While having numerous advantages over metal springs, and although they are capable of absorbing relatively high impact loads imparted thereto, the elastomeric material used to form the draft gear spring tends to respond slower to the relatively high compressive forces applied thereto than metal springs. That is, elastomeric springs used in draft gears are typically slower than metal springs in returning to their nominal or original working form after absorbing a relatively high impact load. As such, and in reaction to a relatively high impact load being applied thereto during the course of normal operation of the draft gear, the inability of the elastomeric spring to quickly return to its original shape adversely affects the positioning and relationship of the metal friction shoes within the inner tapered friction bore of the draft gear housing. As such, and when another relatively high impact or force is directed against the draft gear before the draft gear spring can totally recover from the previous impact load being directed against it, the overall performance of the draft gear is affected.
The railcar draft gear is arranged within a pocket in the railcar and extends generally parallel to a longitudinal axis of the railcar. Accordingly, when the railcar travels through a curve, the railcar tends to impart unequal forces to a free end of the wedge or actuator extending beyond the housing of the draft gear. Such unequal forces applied to the free end of the wedge or actuator on the draft gear are also transferred to the friction members or shoes which tends to cause some shoes to slide axially inwardly relative to the free end of the draft gear more than others. The spring seat of heretofore known railcar draft gears cannot and does not compensate for the unequal axial displacement of the friction members during performance of the draft gear which also results in undesirable overall performance of the railcar draft gear.
Thus, there remains a continuing need and desire to provide a railcar draft gear which is economically designed to have high shock absorbing capacities and capabilities while offering enhanced performance.